A US Marine was killed and 21 others injured when a military aircraft suffered a "hard landing" during routine training in Hawaii, according to the U.S. Marine Corps.The wounded were shifted to a hospital, said spokesperson Captain Brian Block, without specifying the severity of their condition, Efe news agency reported. Block said the cause of the accident on Sunday was being investigated. US media published pictures of the accident in which the tilt-rotor MV-22 Osprey of the 15th Marine Expeditionary Unit was emitting thick smoke and appeared to be on fire. The Marines departed from San Diego, California, on May 10 for a seven-month deployment to the US Armed Forces' Central Command and Pacific Command areas. The MV-22 Osprey aircraft can land and take off like a helicopter, but has wings that allow it to fly like a conventional airplane too.